Question 21 of 28: Non-Functional Requirements for Human-Machine Interfaces
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
98-Comp-B11 Advanced Software Design — National Exams, May 2016. 3 hours, closed book exam with one aid sheet allowed (written on both sides), no calculator permitted. The paper is organized into five parts, and candidates were instructed to answer any five (5) questions in Part I, any three (3) in Part II, any four (4) in Part III, any two (2) in Part IV, and any five (5) in Part V — only the first questions answered, in each part, as they appear in the answer book are marked. All questions carry equal weight, so the 19 questions actually marked (5+3+4+2+5 of 28) each count for 100/19 ≈ 5.26% of the paper. All 28 questions are answered below for completeness.
Reference texts: Sommerville, Software Engineering (10th ed., Pearson) — software processes, requirements engineering, agile methods, design principles, dependability; Pressman, Software Engineering: A Practitioner's Approach (9th ed.) — supplementary process and quality coverage; Gamma, Helm, Johnson & Vlissides (GoF), Design Patterns: Elements of Reusable Object-Oriented Software — creational/structural/behavioural pattern catalogue (Singleton, Proxy, Template Method, Observer, etc.); Sebesta, Concepts of Programming Languages (12th ed.) — polymorphism, dynamic binding, inheritance and language-level object semantics; Bertrand Meyer, Object-Oriented Software Construction — design by contract, preconditions/postconditions/invariants, the open–closed principle; Barbara Liskov's 1987 substitutability paper for Question 11; Rogers, Sharp & Preece, Interaction Design, and Nielsen, Usability Engineering, for Question 21's HMI-specific non-functional requirements; Myers, The Art of Software Testing, for Question 28's boundary value analysis.
PART I — General Principles (answer any 5 of 7)
Question 21: Non-Functional Requirements for Human-Machine Interfaces (Part IV)
The paper prints the first word of this question as "Site" rather than "State"; "State" is adopted here.
Usability/learnability. A new or occasional user must be able to accomplish a defined task within a stated time/error budget without prior training (Question 3's quantification pattern applied to the HMI). Example: "a new user shall complete a standard order-entry task within 5 minutes with no more than one recoverable error." Design strategy: consistent, platform-standard widget conventions plus progressive disclosure (surface common actions prominently, hide advanced options behind a secondary menu) and contextual tooltips, validated through usability testing with representative users.
Responsiveness (perceived). Distinct from the raw system response-time NFR of Question 18: the interface must provide feedback within a bounded, perceptible time even when the underlying operation itself takes longer — e.g., feedback within roughly 100 ms is perceived as instantaneous, per standard HCI response-time guidelines. Design strategy: asynchronous processing with an immediate acknowledgement (a spinner or progress indicator) that decouples perceived UI responsiveness from actual backend operation latency, rather than blocking the UI thread until the operation completes.
Accessibility. The interface must remain usable by users with visual, motor, or hearing impairments — e.g., a stated WCAG conformance level and full keyboard-only operability. Design strategy: complete keyboard navigability (no interaction possible only via mouse), screen-reader-compatible semantic markup/ARIA labelling, and sufficient colour contrast with resizable text, validated against WCAG 2.1 AA success criteria.
